Grounding system for a cabinet

ABSTRACT

A grounding system for cabinets containing electronic equipment is made up from vertical bars (2), horizontal bars (3) and connection bars (11) between the horizontal bars, all the bars being made of aluminum. At the connection points between the bars there are mounted contact-making, spring-biased contact plates (4). The contact plate (4) is rectangular and provided with contact tongues (6) arranged in rows projecting from, both faces of the plate.

FIELD OF THE INVENTION

The invention relates to a grounding system for cabinets containingelectrical equipment and particularly to cabinets containing bars ofsoft metal such as aluminum for carrying off ground currents.

BACKGROUND

When electronic equipment is placed in cabinets, there is therequirement that ground currents, which can be considerable, shall beled off with a rise in potential which is so small that the sensitiveelectronic equipment is not damaged. One kind of ground connection usedso far, comprises conductors with cable shoes placed between theapparatus and their stands, the shoes being screwed to the apparatus andto the stand. Another kind of ground connection comprises a serratedwasher placed between the apparatus casing and the plates of the stand.A fastening screw which fastens the apparatus to the stand passesthrough this serrated washer. An example of such a contact means isdescribed in SE-C-7509869 9(387201).

SUMMARY OF THE INVENTION

The invention is directed to a further development of the abovementioned serrated washer. The invention is characterized by aconstruction in which first and second bars of a yielding soft material,such as aluminum serve for leading off ground currents, the bars beingattachable to a cabinet adapted for containing electrical equipment inan arrangement in which the first and second bars overlap one another,and a contact-making spring-biased contact plate is disposed between thebars at the locations where the bars overlap one another. The contactplate has a plurality of spaced contact points at which contact is madebetween the contact plate and the bars, the contact plate being insertedin an opening in a second plate disposed between the bars to maintainthe contact between the contact plate and said bars at discretelocations constituted by said spaced contact points.

In the grounding system, the bars which are connected to each other, andtogether thus have conductive capacity which is so great that occuringground currents are led away with only a resulting small rise inpotential, and the spring-biased contact plates at the junction pointsbetween the bars give a continous, low transfer resistance between them,although the material of the bars is of soft metal, in this casealuminum, which yields somewhat to compression stress.

The horizontal bars in side-by-side cabinets are united by connectionbars of aluminum with the aid of the same spring-biased contact platewhich unites the bars in the cabinet.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

An example of a grounding system in accordance with the invention isdescribed in the following with reference to the accompanying drawings,wherein:

FIG. 1 diagrammatically illustrates two cabinets with bars;

FIG. 2 illustrates a junction point between a vertical and horizontalbar

FIGS. 3 and 4 illustrate a spring-biased contact plate in side view andelevation view respectively;

FIG. 5 illustrates a contact plate inserted at an intersection pointbetween bars; and

FIG. 6 is an exploded view which illustrates a connection bar betweenhorizontal bars.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF INVENTION

Two cabinets 1 are illustrated as an example in FIG. 1, each containingtwo vertical bars 2 and two horizontal bars 3. Each vertical bar 2 isbent towards at right angles at each end, and in each cabinet there isan unillustrated connection terminal arranged on one of the bent-inparts for the connection of a ground conductor. Any of the four bent-inparts may be used for connecting the ground conductor.

A contact plate 4 is disposed, as illustrated in FIG. 2, at anintersection point between one of the vertical bars 2, and one of thehorizontal bars 3. The vertical bar 2 has a rectangular cross sectionand is attached to the side wall of the cabinet by fastening screws (notshown), while the horizontal bar 3, which is carried by a surroundingplate 5, is fastened to the cabinet with other fastening screws andpressed against the narrow edge of the vertical bar.

As illustrated in FIGS. 3 and 4, the contact plate 4 has a rectangularshape, punched out from sheet metal, and is provided with a plurality ofcontact tongues, four in the illustrated example, which are punched outin a row along the center line of the plate and alternatingly bent outof the plane of the plate so that there is formed a total of eightcontact-making edges 7. The edges 7 are right-angular and sharp to givegood electrical contact with the bars.

A small part of the ends 8 of the contact plate is somewhat bent outfrom one face of the plate to form retaining flanges.

The material of the contact plate 4 is tin bronze and is tinned, wherebythe plate will give durable electrical contact against the aluminum barswithout any danger of corrosion. Alternatively, the contact plate may bemade from some other similar material, e.g. beryllium copper.

As previously mentioned, and as will be more clearly perceived from FIG.5, the contact plate 4 is inserted in an opening in the plate 5 and isthere pressed between the vertical bar 2 and the horizontal bar 3. Theretaining flanges 8 of the contact plate are urged against the edges inthe opening of the plate 5 so that the contact plate will be preventedfrom falling out during assembly, and the contact tongues 6 are bentsuch that the width of the contact plate measured between the edges 7 isgreater than the space between both bars, such that the contact edgeswill engage against the bars with a continuous pressure after insertion.Since the contact plate 4 is disposed in the plate 5 the contact tongues6 are prevented from being completely pressed together.

In the grounding system of the invention, there is further included, aswill be seen from FIGS. 1 and 6, a connection bar 11 for connecting thehorizontal bars 3 in side-by-side cabinets. As for the other bars, thematerial of the connection bar 11 is aluminum and its cross section issubstantially rectangular with two flanges at the edges of the bar, sothat its cross section has the form of a shallow U. At the ends of theconnection bar, two spaced nodules 12 are pressed into the bar along itscenter line. The nodules and the flanges of the bar are adapted toretain one contact plate 4 at either end of the bar 11.

The horizontal bar 3 is provided with a longitudinal groove 13 with awidth and depth suited to the reception of the connection bar 11 withits accompanying plate 4 in the manner illustrated by a curved arrow inFIG. 6. The thickness of the horizontal bar 3 is adjusted in relation tothe width of the groove 13 so that the contact tongues on the contactplate 4 are prevented from being completely pressed together.

To enable mounting the connection bar 11, the cabinet 1 is provided witha plurality of openings (not shown) at different heights in the sidewalls of the cabinets.

The horizontal bars 3 and indirectly the vertical bars 2 also, in two ormore cabinets are electrically connected to each other with one or moreconnection bars 11, whereby any ground currents are effectivelydistributed in the bars and are led away to the ground conductorsconnected to each cabinet, so that potential rises are limited to avalue which is not dangerous.

Electronic placed in the apparatus cabinet 1 are each provided with aground conductor intended for connection to one of the horizontal bars3, preferably with a connection means of the kind described inSE-C-7509890-5 (387480) and which is intended for attachment by a screwengaged in the groove 13 of the horizntal bar.

What is claimed is:
 1. A grounding system for cabinets containingelectrical equipment comprising first and second bars of a yielding,soft metal for leading off ground currents, said bars being attachableto a cabinet adapted for containing electrical equipment in anarrangement in which the first and second bars overlap one another and acontact-making, spring-biased contact plate between the bars at thelocation where the bars overlap one another, said contact plate having aplurality of spaced contact points at which contact is made between thecontact plate and said bars, the contact plate being inserted in anopening in a second plate disposed between the bars to maintain thecontact between the contact plate and said bars at discrete locationsconstituted by said spaced contact points.
 2. A grounding system asclaimed in claim 1 wherein said contact plate comprises a flat plateelement having contact tongues arranged in a row and projecting fromboth sides of the contact plate.
 3. A grounding system as claimed inclaim 2 wherein said contact tongues are bent outwards from the contactplate in alternating opposite directions.
 4. A grounding system asclaimed in claim 3 wherein each tongue has opposite ends respectivelyforming said contact points.
 5. A grounding system as claimed in claim 4wherein said contact plate element has opposite ends and portions atsaid ends bent out from the plane of the contact plate to form retainingflanges.
 6. A grounding system as claimed in claim 5 wherein saidcontact plate is made of tin bronze.
 7. A grounding system as claimed inclaim 5 wherein said first and second bars are respectively arrangedhorizontally and vertically, said system further comprising an aluminumbar for connecting the horizontal bars of adjacent cabinets together anda further said contact plate between the aluminum bar and each of thehorizontal bars of the adjacent cabinets.
 8. A grounding system asclaimed in claim 7 wherein each horizontal bar has a groove forreceiving said aluminum bar together with the further contact plate. 9.A grounding system as claimed in claim 8 wherein said aluminum bar hasflanges between which said further contact plate is retained.
 10. Agrounding system as claimed in claim 1 wherein said first and secondbars are respectively arranged horizontally and vertically, said systemfurther comprising an aluminum bar for connecting the horizontal bars ofadjacent cabinets together and a further said contact plate between thealuminum bar and each of the horizontal bars of the adjacent cabinets.